In the United States, overall asthma prevalence has increased by 60 percent since 1980, and the increase in asthma hospitalizations is greatest among preschool-age children of Hispanic and African descent living in low-income urban areas. Indoor aeroallergens and irritants are known to trigger asthma exacerbations, but in recent years, preliminary evidence has implicated additional factors associated with modem urban environments and lifestyles as contributing to risk for asthma. These risk factors are obesity and physical inactivity, which are similar to asthma in descriptive epidemiology and appear to heighten bronchial reactivity, and lack of early exposure to infectious agents and/or substances, such as endotoxin, that appear to promote the development of the immune system. Nitrogen dioxide (NO2), an irritant, is also suspect because it enhances susceptibility to some infectious agents. We propose to study the association of these risk factors with the prevalence, persistence, and incidence of asthma or asthma-like conditions over a three-year period in a cohort of children entering Head Start programs in high-risk neighborhoods in New York City, including those exposed to airborne particulate matter from Ground Zero. Our study will begin with a telephone survey of asthma symptoms and risk factors among parents of 2000 3-4-year-olds entering Head Start programs in neighborhoods with >20 asthma hospitalizations per 1000 preschool-age children per year. From the respondents, we will recruit a cohort of 1000 for 2 annual follow-up telephone interviews; of these 500 will also receive 3 annual home visits to measure endotoxin, aeroallergens (cat, mouse, and cockroach), and NO2 in the home, and height, weight, physical activity, and pulmonary function in the child. Blood specimens collected annually from the child and once from each parent will be analyzed for antioxidant levels, cotinine, and total and specific IgE. We will also conduct environmental sampling within the Head Start centers twice a year. Our goal is to identify risk factors that interventions can target to lighten the burden of asthma on school-age children.